Television

From the collection of the

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San Francisco, California
2006

TELEVISION

COMPILED BY WORKERS OF THE
WRITERS' PROGRAM OF THE WORK
PROJECTS ADMINISTRATION IN THE
COMMONWEALTH OF PENNSYLVANIA

ALBERT WHITMAN
& 4-co

CHICAGO 1942

PENNSYLVANIA DEPARTMENT OF PUBLIC INSTRUCTION

State-wide Sponsor of the
Pennsylvania Writers' Project

FEDERAL WORKS AGENCY
John M. Carmody, Administrator

WORK PROJECTS ADMINISTRATION

Howard 0. Hunter, Commissioner

Florence Kerr, Assistant Commissioner

0. K. Yeager, Acting State Administrator

Co-sponsored and copyrighted, 1942, by Division of Extension Education
Board of Public Education, Philadelphia

FOREWORD

Television is the twenty-seventh booklet in
the Elementary Science Series. It was pre-
pared by the Pennsylvania Writers' Project
which is sponsored by the Pennsylvania De-
partment of Public Instruction. This booklet
was written by Katharine Britton. Illustra-
tions were drawn by Reynolds Mason of the
Pennsylvania Art Project, under the direction
of Michael Gallagher.

Acknowledgment is made to William P. West,
Associate Director in charge of Electric Com-
munications, Franklin Institute, Philadelphia,
for acting as consultant to assure accuracy of
the text and illustrations.

J. KNOX MlLLIGAN

State Supervisor

TELEVISION

football game. A prize fight. A
ballet dance. A swing orchestra. A
play, Death Rides the Range. A trip
through the Metropolitan Museum of Art.
All these and many other colorful things
a person can see and hear during one
week in his own living room. And he can
see them at the same time that they are
actually happening many miles away.
Is the person who can see such things a
magician? Does this seem like some-
thing that could happen only in a dream?
It is no dream story. This list of events
was taken from a newspaper. It is part
of a program of television broadcasts.
Anyone who lives near New York and
owns a television set may really have
seen these very things, and many more, in
one particular week.

5

Television is so new and so strange that
all of us can still feel the wonder of it.
To be able to see far-distant things as they
happen was one of the oldest desires of
men. For a long time it seemed no more
than a dream. People believed it could
come true only in story books, or by
magic.

But it is not magic. It is the result of
men's work. We have it today only be-
cause of men's studies and discoveries
during hundreds of years. Little by little
men gathered knowledge about the world
around them and the forces of Nature.
At last, just a few years ago, by using this
fact and that from their store of knowl-
edge, they were able to create the wonder
that we know as television.

The word television is made up of two
words. The last part of it we are familiar
with. Vision means sight. Tele is a
Greek word that means far off. So tele-
vision is seeing things happening at a
distance.
6

Let's stop and think what this really
means. Certainly we don't see the actual
events happening in distant places. We
see moving pictures of them. These pic-
ture messages have been carried to us so
quickly that we see them almost as soon
as do the people on the scene. They are
carried by radio, a messenger swifter than
lightning. So we must know something
about both radio and moving pictures to
understand how it is done.

RADIO

A man speaks in Washington and his
voice is heard in a split second throughout
the United States. That no longer seems
wonderful to us. We say that the radio
does it. But certainly it is a strange
thing that our radios should be able to
pick this message out of the skies. There
is no connection at all between them and
the man in Washington. Why does this

far-away voice make our radios speak if
they are tuned to the right station?

The message of the voice is carried to
us by radio waves. These are waves that
cannot be seen or felt. Yet it will not be
very hard for us to understand them, for
in some ways they act like waves in
water. By watching water waves we can
find out many things about radio waves.

Suppose the tub in the bathroom is
filled with water. At one end of the tub
a cake of soap is floating. Now someone
moves a stick up and down in the water
at the other end. The water around the
stick begins to move up and down in little
waves. The waves spread out farther
and farther. When they reach the cake
of soap, this too begins to move up and
down in time with the stick.

If the stick is moved up and down more
rapidly, the soap moves more rapidly too.
If the stick is plunged deeper, the soap
moves farther down and farther up. It
8

always moves just as the stick moves.
For as the motion of the stick is changed,
the waves are changed, and they change
the motion of the soap.

THE CAKE OF SOAP MOVES UP AND DOWN IN TIME WITH THE

STICK.

The person with the stick can even send
simple messages to someone else by figur-
ing out a code. Perhaps moving the stick
fast means, "I feel happy, How are you?"

9

Moving it slowly may mean, "I am tired.
Let's stop playing."

By keeping his eyes on the soap, the
second person can tell what his friend is
saying even though he doesn't look at the
stick. And if the person with the stick
learns to move it so as to change the
waves just as he wishes, many more
messages can be worked out.

In somewhat the same way, radio waves
are made by electricity surging up and
down in the antenna at a broadcasting
station. The electricity surges up and
down thousands or even millions of times
a second. Each up and down surge is
called a cycle, and sends out a radio wave.

The radio waves spread out in all direc-
tions from the broadcasting station. They
move very much faster than water waves.
In one second they travel 186,000 miles!
That is fast enough to go all the way
around the world more than seven times
a second.
10

In any receiving set that is tuned in
properly, the radio waves make electricity
surge back and forth in time with the
electricity surging in the sending set at
the broadcasting station. If the station
is sending out one million waves a second,
the electric current in all these radios
flashes back and forth one million times
a second. It also grows stronger or weak-
er as the current in the sending set grows
stronger or weaker.

Sometimes the message is sent by
changing the number of times a second
the electric current in the broadcasting
station surges up and down. Sometimes
it is done by changing the strength of the
surging current.

Suppose a radio station is broadcasting
a play. The actors speak their lines
into a microphone, which works like the
mouthpiece of a telephone. The sound
makes the current of electricity flowing
through the microphone move in waves

11

that grow stronger or weaker, or some-
times almost die away entirely. This
gives its pattern to another electric cur-
rent, which is surging back and forth in
the sending set. Out upon the air flow
radio waves bearing the same pattern of
changes as the electricity flowing from
the microphone.

Through the skies the waves flash.
They set up a current with the same pat-
tern of changes in our radios. Then this
current is changed back into sound by
our radio loud-speaker, which works much
like the receiver of a telephone. And we
hear the actors read the lines of the play.
Electric current can be changed in dif-
ferent ways in order to send different
kinds of messages. Men found out how
to send sound messages by radio a long
time before they found a way to send
picture messages over the air.

Anyone who wants to learn more about
radio waves and how they are used may
12

read the book called Radio in this same
Elementary Science Series.

RADIO PICTURES

To send a sound message by radio the
sounds must first be changed into electric
current. In the same way, to send a pic-
ture, light must be changed into electric
current. For a picture or a scene is really
many small areas of light, some brighter,
some darker.

Changing light into electricity is not so
difficult as it might seem. A number of
years ago men discovered that certain
materials found in nature produced elec-
tricity whenever light rays struck them.
The amount of electricity produced de-
pends on the brightness of the light. A
strong light makes a large current of
electricity. Weak light makes a smaller
current. In darkness no current at all
is produced. Such materials are called

13

photo-electric. Photo comes from a
Greek word meaning light.
Men had found too that the electricity

THIS IS ONE KIND OF PHOTO-ELECTRIC CELL.

produced in photo-electric material can
be drawn off through electric wires. The
amount of electricity flowing through the
wires changes as the amount of light fall-
ing on the photo-electric material changes.

Men put their knowledge of photo-
14

electric materials to use in many ways.
For one thing, they invented what is
called a photo-electric cell. This is one

PHOTO-ELECTKIC CELLS ARE USED IN OPERATING THESE DOORS.

of the most wonderful of all of today's
inventions.

Some photo-electric cells look much like
electric bulbs. Each has a metal plate
inside the glass and this is coated with

15

photo-electric material. There is an ar-
rangement of wires to lead off the electri-
city produced when light enters the cell
and strikes the metal plate.

The photo-electric cell is used in oper-
ating those doors that seem to open of
themselves when we come up to them.
It has many other uses. But a simple
cell cannot be made to carry a message
of a picture. For instance, if a person
should stand before a photo-electric cell,
he would cast a shadow on the cell. This
would change the amount of electric cur-
rent flowing through the wires, but the
whole image of the person would affect
the cell at once. There would be no way
of telling from the amount of current
produced what the different parts of the
person's face were like.

The men who were working on tele-
vision had a very clear idea of what they
had to do to send a picture message with
a photo-electric cell. They had to find
16

some way of making the cell measure the
light from each part of the picture
separately.

EVERY PICTURE IS MADE UP OF DARKER AND BRIGHTER AREAS.

To understand exactly what this means,
let us get a picture from the newspaper
and cut it up into many parts, as fine as
possible. Then if we pick up the pieces

17

one by one, we can no longer tell which
part of the picture each one conies from.
The only difference among them is that
some are darker, some brighter.

If Mother decided now that we must put
the picture together again, we should
really be in a nice fix. We shouldn't be
able to do it no matter how long and hard
we tried.

Yet this is just about the problem that
the television men had to face. They not
only had to find some way of changing the
light from each part of the scene or pic-
ture into changing electric current or
electric waves; they also had to have some
way of keeping the electric waves in the
proper order. Then the electricity could
be changed back into small dots of light
arranged so as to form the picture.

One way of sending photographs by
means of the photo-electric cell is this:

The film of the picture to be sent is

18

wrapped around a glass cylinder. A cyl-
inder is shaped like a tin can. But the
cylinder holding the picture is much
larger than an ordinary tin can. This
cylinder turns around and around on a
pole. At the same time, it moves lower
on the pole little by little, just as a nut
turns on a screw.

When the glass cylinder first starts to
move, a very bright ray of light from an
electric lamp is pointed at one spot on the
bottom of the picture. This ray of light
remains still, and slowly every bit of the
picture passes under it. We say that the
ray of light has scanned the picture.

Inside the turning cylinder is a photo-
electric cell. The ray of light shines
through the film and the glass upon this
cell. When bright parts of the film are
passing under the ray, a strong light
shines upon the cell. Then the current
from the cell is also strong. But when
the ray passes over darker areas, only a

19

little light shines through, and the cur-
rent from the cell becomes weak.
The changing current from the cell

THIS IS ONE WAY OP SCANNING A PICTURE. THE LIGHT

REFLECTED FROM EACH SPOT OF THE PICTURE SHINES UPON

THE PHOTO-ELECTRIC CELL ON THE RIGHT.

flows through wires or is sent out over
the air by radio waves. At the end of its
journey, there is another cylinder turning
20

exactly in time with the sending cylinder.
Around this second cylinder is wrapped a
piece of fresh film. In front of the cylin-
der is a special kind of electric bulb,
which casts a ray of light on the film.
The changing current sent out from the
first cylinder travels along the wires of
this bulb. As the current becomes
stronger or weaker, the ray of light
flickers, becoming brighter or dimmer.
And as it flickers, it makes changes in the
film on the cylinder just as light makes
changes on film in a camera. It really
makes a picture.

This method of scanning a picture
works very well, and it gives a very true
image. But it takes about eight minutes
to send one picture. For this reason it
cannot be used in television. For the
moving pictures that we see in television
are really separate pictures. Thirty of
them are flashed on the television screen
every second.

21

MOTION PICTURES

If one happens to know something
about motion pictures, this will be less
surprising. For moving pictures on the
theater screen are also separate pictures,
flashing one after the other before our
eyes.

There is no camera that could take
pictures in which the people or things are
actually moving about as we watch.
They only seem to be moving. The cam-
era takes thirty different pictures of a
scene every second. In each picture the
scene is shown just a little differently
from the one before it. It may take ten
pictures for a man to make one step.
But when these pictures are run off before
us at the rate of thirty a second, we see
them all as one moving picture.

The reason for this strange thing is
that our eyes hold any picture message
for about one-tenth of a second. By the
time one picture has faded from our eyes,
22

another has taken its place on the screen,
and we do not see them separately.

There is a simple way of showing how
this happens. On one side of a white
card draw an animal. On the other side
of the card draw a cage Now tie a string
to the center of the card at the top and
another to the center at the bottom.
Hold the card by two strings and blow on
it so that it whirls around and around.
The animal looks as though it were in the
cage. This is an illusion. An illusion
is something that seems to be different
from what it really is.

The picture on a moving picture screen,
or a television screen, also gives us an
illusion. It is called the illusion of mo-
tion. Another book in this series, called
Motion Pictures, tells a great deal more
about this and the other ideas used in
motion pictures.

23

THE SCANNING DISK
Since a number of pictures must be
sent out every second in order to televise
a scene, the scene must be scanned very,
very quickly. The first successful way
of doing this was shown to the world in
1925. Besides the photo-electric cell, this
method used what is called a scanning
disk. The scanning disk itself was not
new. The idea was first worked out
forty years before that by a man named
Paul Nipkow.

A disk is anything that is round and
flat, like a plate or a phonograph record.
The scanning disk has a number of holes
cut in it, placed like those in the picture
on this page. Each hole is just a little
bit closer to the center of the disk than
the hole before it. The disk faces the
scene to be televised and whirls around
and around like an electric fan.

Behind the disk is a very bright light.
This light shines through the whirling
24

holes. First the outside hole whirls by,
and the light moves like a pencil over the
top of the scene. Then the next hole

THIS MAN IS LOOKING IN AT THE SCREEN OF A SCANNING DISK
RECEIVING SET.

whirls by, and the beam of light flashes
across another section of the scene, just
below the first. When sixty holes have
whirled by, the whole scene has been

25

scanned once. Then one whole picture
has been sent out.

The disk is moving rapidly enough to
send out perhaps thirty pictures a second.
The beam of light moving across the scene
is reflected now strongly, now weakly,
depending on the brightness or darkness
of each picture of the scene. These
changing reflections are picked up by two
sets of photo-electric cells. From the
cells flow a changing current of electri-
city, to be sent out over wires or changed
into modulated radio waves.

The receiving set has a disk with holes
placed just like those in the disk at the
television station. The two disks whirl
in exact time with each other. Behind
the receiving set disk is an electric bulb
whose light shines through the holes
upon a small screen. The beam of light
flickers as the changing current flows
through the electric bulb. This flicker-
ing beam of light paints thirty pictures
every second upon the screen.
26

Of course the person watching the
screen doesn't see the pictures being
made, and he doesn't see them separately.
His eyes are too slow. What he sees is
the scene that is being broadcast, or as
we say, telecast.

THESE DRAWINGS SHOW HOW A PICTURE BECOMES CLEARER
AS THE NUMBER OF SCANNING LINES BECOMES GREATER.

By learning how the scanning disk
works, we can understand many of the
ideas that are used in television. Then
we shall understand more quickly the
system of television now in use in
America.

TELECASTING IN AMERICA TODAY

The scanning disk system has several
big faults. For one thing, it has moving

27

parts. They wear out quickly or get out
of order and must be repaired. Another
trouble is that the electric light behind
the disk in the receiving set is a neon
light. This is the kind of light used to
light many signs at night. Neon light is
bright pink or red in color. So the mov-
ing pictures in the television screen are
pink and black instead of white and
black. This not only looks strange to the
person watching, but it makes his eyes
very tired.

Besides this, the pictures telecast by
the scanning disk are not very clear. All
the different small parts in a scene do not
show. This is because the disk breaks
up the scene into only sixty to ninety
strips. So all the differences of light and
shadow in the scene cannot be caught.

Because of these things, many people
believed that it would never be possible
for television to become as important in
our lives as radio has become. Yet today
28

we have a system so good that it has
already brought television into many
homes.

In this new system, the scanning is
done inside a very special type of camera
called a television camera. On the out-
side, the television camera looks much
like a very large newspaper camera. It
is a box-like thing that stands on three
legs. It has a "glass eye" in front like
any other camera. But inside it is very
different.

The thing that makes the television
camera different is an invention called
the iconoscope. The iconoscope is a large
glass bulb from which almost all of the
air has been removed. The light from
the scene being televised enters the icono-
scope through the glass eye of the camera.
It strikes a square metal plate in the back
of the iconoscope. This metal plate is
covered with millions of tiny particles of
photo-electric material. Each of these

29

tiny particles at once produces a certain
amount of electricity, depending on the
amount of light that falls on it. The
scene before the camera has been cap-
tured in an electric picture.

Down in the narrow neck of the icono-
scope is something called an electron gun.
This electron gun shoots a stream of
electricity at the metal plate just as a
garden hose sprays water on the lawn.
This stream of electricity moves left across
the top of the metal plate. Then^ it
moves back to the other side along a
path slightly below the first one. Back
and forth it goes like this, until every bit
of the metal plate has been scanned.

This moving stream of electricity,
called an electron beam, strikes the tiny
photo-electric particles one after the other.
As the beam strikes each one, a certain
amount of electricity flows from the metal
plate. This is called one signal. Each
signal moves along through the wires
30

leading to the transmitting set, which
will send out the radio waves over the
air. The strength of a signal depends of
course on the amount of electricity that
the light from the scene has left in each
photo-electric particle.

The electron beam moves back and
forth 525 times for each picture. Along
each of the 525 lines it sends out several
hundred signals of different strength.
Since the beam scans the whole metal
plate thirty times every second, it sends
out a million or more signals every second.
It has to move very rapidly to do this.
From left to right it moves at a speed of
two miles a second. Returning from right
to left it moves twenty miles a second.
That is a speed of 72,000 miles an hour.

Along the wires leading to the trans-
mitting set flashes the changing electric
current, bearing these millions of signals.
There the pattern of the signals is given
to another electric current, which is al-

31

ready surging back and forth millions of
times a second. The radio waves made
by the surging current carry the message
of the signals through the sky. They are
picked up by any television receiving set
that is close enough and is tuned in
properly.

THE TELEVISION RECEIVING SET

A television receiving set has many
more tubes than an ordinary radio set.
Some of these tubes strengthen the surg-
ing current produced by the radio waves
sent out from the television station.
Otherwise this current would be much
too weak to produce a good picture. The
radio waves bearing the signals become
weaker the further they spread out from
the broadcasting station.

Other tubes act in such a way that
when the current leaves them it is flowing
in waves just like those that flowed from
the millions of tiny photo-electric cells in

the television studio.
32

Besides all these tubes, there is one big
glass tube. The task of this tube is to
change electric current back into light
and so make pictures. Like the icono-

LUMINESCENT SCREEN

scope, the tube has an electron gun down
in its narrow neck. The top of the tube is
flat. It is made of a material that acts
just the opposite from photo-electric ma-
terial. Instead of producing electricity
when light falls upon it, this material

33

gives out light when electricity strikes it.
In other words, it is luminescent. This
luminescent material forms the screen on
which the moving pictures are produced.

The current in the receiving set, flow-
ing just like the current sent out from the
iconoscope, makes the electron gun shoot
a beam of electricity at the screen. This
beam changes exactly as the current
changes. It moves in time with the beam
in the iconoscope. When the electron
gun is shooting at a certain spot on the
metal plate of the iconoscope, and a
strong current is flowing from that spot,
the beam of the electron gun in the
receiving set is shooting a beam of elec-
tricity of exactly the same strength at
exactly the same spot on the screen of
the receiving set.

The beam of electricity, changing in
strength as it moves back and forth
across the screen, makes each spot that
it touches glow. The brightness of the
34

glow depends on the strength of the beam.
And so a picture appears on the screen, a
picture of the scene that is being telecast.

TELEVISION IN COLORS

At first only black-and-white pictures
could be sent by television. The icono-
scope could not separate the different
colors of the scene. The television re-
ceiving set was color-blind.

That is no longer true today. Men
know how to capture all the colors in a
scene and send them over the air. They
are still testing out this idea, and color
receiving sets are not yet in use in our
homes. But it is quite possible that some
day all television moving pictures will be
in natural colors.

To send color pictures something new
had to be added to the television camera.
There was no way of making the photo-
electric particles in the iconoscope see all
the different colors in a scene. They

35

could measure only the amount of light
that struck them, not the color of that
light.

The new part of the color television
camera is an arrangement of three thin
sheets of a material that looks like gela-
tin. It actually is gelatin prepared in a
special way. Through these sheets of
gelatin light can pass. One sheet is red,
another blue, another green. They are
called filters.

The three filters revolve before the
metal plate of the iconoscope. First one,
then another, then the third passes before
the plate. The electron gun scans the
metal once while the red filter is before it.
Then it scans the plate while the green
filter is before it, and again when the blue
one is before it.

The light passes differently through
each of the colored filters. So the mes-
sage sent out through each one is slightly
different from the other two. The three
36

different picture messages are going to be
put together in the television receiving
set to make one single colored picture.

Because each group of three pictures
taken through the revolving filters makes
only one color picture, the electron beam
has to work very rapidly. Instead of send-
ing out thirty pictures a second it must
send out three times as many, or ninety.

In the television receiving set is a disk
made up of three colored filters. This
disk revolves like a phonograph record.
Each filter passes before the screen at
exactly the same instant that the filter of
the same color passes before the icono-
scope plate in the sending station. A red
filter covers the screen of the receiver at
the same time that the iconoscope is send-
ing out the message received through its
red filter.

Through each filter a picture of dif-
ferent color is thrown on the television
screen. But the person watching does

37

not see the separate pictures. Through
his eyes they become one picture, and
even this he does not see as one separate
picture. Ninety pictures, or thirty groups

A DISK MADE UP OF FILTERS OF THREE DIFFERENT COLORS
IS PLACED IN THE RECEIVER SET.

of colored pictures, are flashed before him
in one second, but he sees only a moving
picture in full color.

How can he see full color when only
red, blue, and green filters were used?
38

Well, these three colors have been mixed
to form other colors. We all know some-
thing about how this happens from work-
ing with colored crayons. With just two
or three colors many more can be made.
Blue and red make purple. Blue and
yellow make green. Red and yellow
make orange. In the same way, the
three colors of the filters mix on the
screen to make all the colors of the scene.

WATCHING A TELECAST

A television studio looks much like a
moving picture studio. It is very brightly
lighted. Here and there are pieces of
scenery and many articles of stage
property. Costumes lie ready, so that
changes from one to another can be made
with lightning speed. Three television
cameras are set on small rubber-tired
moving platforms called dollies. On the
dollies the cameras can be moved wher-
ever they are needed. Overhead on a

39

long moving arm is the microphone. This
too can be moved about to follow the
performers. It will pick up the sounds of
the programs at the same time that the

ENGINEERS IN A CONTROL ROOM WATCH TO MAKE CERTAIN
THAT THE TELECAST IS GOING ALL RIGHT.

camera takes the pictures. Then both
sounds and pictures will be sent out to-
gether by radio waves.

The director of a television play or
40

program not only has all the problems of
a moving picture director and a radio
play director. He also has other prob-
lems that neither of them has.

For instance, he has to make certain
by silent signs that his actors do not walk
out of range of the camera. If they do,
the watchers will see them suddenly
disappear from the television screen. So
the floor of the studio is carefully marked
to show the actors just how far they may
go. If a mistake is made, the scene can-
not be done over, as it can in the movies.
The sharp eye of the television camera
will catch the fault and broadcast it to
the world.

Another problem is that sound effects —
like thunder, a railroad train, or an
automobile crash — cannot be made close
to the microphone, as they often are in
ordinary radio. The sound effects man
must keep his strange contraptions out
of the way, so that they cannot be seen

41

by the cameras. Sometimes the sounds
have to be made in a different room.
Then they are matched, or synchronized,
with the telecast in the control room.

One of the most difficult problems of all
is finding suitable actors. Of course, the
actors must be able to do the parts well.
They must have the right voices, and the
right appearance. But that is not all.
Television actors must also be the right
size. They have to be rather small and
thin. Anyone large or tall looks like a
giant on the small television screen, and
the other characters look like dwarfs
beside him.

Besides that, the actors must be dark-
haired. The darker the hair the better
it televises. Sometimes the head of a
very blond person does not televise at all.
Usually the blond head appears, but there
is a circle of pale light around the head
not only of the blond person, but also
around the head of anyone near him. For
42

this reason blondes are known in tele-
vision as blizzard heads.

Blondes cannot even help matters by
dyeing their hair. Dyed hair televises
muddy and dead-looking.

One thing that is no problem for the
director today is the makeup of the per-
formers. In the early days, however,
this was one of the worst problems. The
television camera was so poor that it
caught only very great differences in light
strength. So the actors had to cover
their faces with heavy white grease.
Their lips were painted black and their
eyelids were painted very dark. This
made them look so strange and funny
that it was hard for them to act well.
Even with this heavy make-up, the lights
had to be very very bright. They gave
off so much heat that the actors became
very warm and perspired under their
heavy make-up.

Today the television camera sees even
44

very small differences of light. Besides
that, the lights in the studio have been
made much better. It is possible to get
very brilliant lights that produce little
heat. For these reasons, no more make-
up is needed than a girl would wear on a
bright sunshiny day outdoors.

BEYOND THE HORIZON

There is one problem of television that
has not yet been solved. Men have not
found a way to telecast very long dis-
tances at low cost. The radio waves used
in television act somewhat differently
from those used in ordinary broadcasting.
They are very short waves. This means
that the distance between the crest of one
wave and the next is small. The shortest
radio waves are no longer than the dis-
tance a child could throw a rubber ball.
The waves used in regular radio broad-
casting are from a few yards to three city
blocks long.

45

Longer waves travel along following
the earth's curve. But short waves travel
more in a straight line. They are gen-
erally lost beyond the horizon, as the

TELEVISION -Ultra Short W«ve

THE SHORT WAVES USED IN TELEVISION ARE LOST BEYOND
THE HORIZON.

diagram on this page shows. The hori-
zon, of course, is the place where the earth
meets the sky. The short waves used in
long-distance radio broadcasting bounce
back to earth again very far from where
46

they started. But the very short tele-
vision waves do not do this.

Usually television waves carry their
message fifty or sixty miles. Sometimes
they carry it one hundred miles. The
only way today to carry television pic-
tures much farther without using wires
is to build what are called booster sta-
tions about fifty miles apart. These
booster stations can pick up the waves,
strengthen them, and send them on the
next lap of their journey. The only
trouble with this plan is that it is costly.

Yet it is very likely that within twenty
years or so men will find a simple way to
send television broadcasts as far as radio
broadcasts. We know that this may be
possible because once some very faint
pictures from a program telecast in Eng-
land were picked up on the Atlantic
coast of America. At other times strange
pictures from across the seas were seen
in testing stations in our Far West.

47

No one has yet found out exactly why
these television broadcasts carried so far.
But men will keep on testing and trying
to find out, until they do discover what
caused these freaks. Then they may dis-
cover also a way to repeat the strange
happenings whenever they wish.

The mystery of the freak telecasts
shows how far men have still to go before
they learn all the secrets and all the uses
of radio waves. But it is thrilling to
think about the exciting adventures that
lie ahead in this search, and the wonder-
ful things it may bring about.

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